In this project chemically reactive and water soluble macromolecules have been synthesized and their effects on mammalian cells in culture studied, mainly emphasizing the study of their interaction with the cell membrane. Polysaccharides, dextran, plant gums and modified peptides, which are neither bound nor consumed by cells, were used as carriers for various chemically reactive groups. The resulting macromolecules have been tested in vitro on mouse erythroleukemic cells and on human fibroblasts.